KR20010019546A - Plannar light waveguide element and method of fabricating the same - Google Patents

Abstract

PURPOSE: A planar optical waveguide device and method of fabricating the device are provided which deposits a silica thin film on a lower cladding layer and an etched surface of a core to restrict diffusion of impurities, thereby minimizing waveguide transformation. CONSTITUTION: An optical waveguide device includes a planar substrate(10), a lower cladding layer(12) deposited on the flat substrate, and a passivation layer(14) deposited on the lower cladding layer to minimize transformation generated at the interface. The device further has an optical waveguide formed of a material having refractive index larger than that of the lower cladding layer on the passivation layer, and an upper layer(20) deposited on the optical waveguide and the passivation layer.

Description

TECHNICAL FIELD [0001] The present invention relates to a planar optical waveguide device, and a planar optical waveguide device,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light waveguide, and more particularly, to a plannar light waveguide element having a passivation layer and a method of manufacturing the same.

Recently, many researches have been made on the integration technology of optical devices that fabricate optical waveguides on flat substrates by using plane waveguide technology for optical signal processing such as branching, modulation, switching, and signal multiplexing of optical signals. Examples of technologies required for fabricating such an optical waveguide device include waveguide design, fabrication, package, and the like.

A general optical waveguide is a light transmission line that confines light waves and propagates less loss in the longitudinal direction. It is composed of a core having a large refractive index and a cladding having a low refractive index surrounding the core.

Various methods have been proposed for fabricating the optical waveguide as described above. For example, U.S. Patent No. 5,417,804 (OPTICAL WAVEGUIDE MANUFACTURING METHOD), 5,598,501 (POLYIMIDE OPTICAL WAVEGUIDE AND METHOD OF MANUFACTURING THE SAME), 5,858,051 (METHOD OF MANUFACTURING OPTICAL WAVEGUIDE), 5,872,883 (CURVED OPTICAL WAVEGUIDE AND METHOD OF MANUFACTURING THE SAME, US Pat. No. 5,903,697 (OPTICAL WAVEGUIDE, METHOD OF MAKING THE SAME AND INTEGRATED OPTICAL DEVICE), and the like.

In order to fabricate the planar optical waveguide, a plurality of thin film deposition processes and etching processes are required. In order to control the device characteristics, desired refractive index distributions and waveguide structures should be easily controlled. It is necessary not only to form a desired width and height pattern in the etching process but also to maintain the interface uniformly without being diffused or deformed in a plurality of thin film deposition steps.

Flame hydrolysis deposition (FHD) is the most commonly used method for forming a lower clad layer and a core layer on a silicon substrate. In the FHD method, an oxyhydrogen flame is generated using a torch, and a silica soot is formed by reacting SiCl ₄ , GeCl ₄ , POCl ₄ , BCl _4, or the like in the flame to deposit on a silicon substrate And a sintering process in which the substrate on which the soot is deposited is heated in a sintering furnace to form a transparent glass film. A planar optical waveguide is fabricated through a deposition process and an etching process on a silica substrate manufactured by such a process.

However, in the conventional optical waveguide fabrication process, most of the thin film deposition is performed at a relatively high temperature, and diffusion of the impurities occurs smoothly, so that the boundary is liable to be deformed. Particularly, in the case of the FHD method widely used for the deposition of the silica thin film, since the porosity of the spherical silica particles deposited is very large, the sintering process is performed at about 1000-1300 ° C to make a dense structure. When the waveguide size is large due to the diffusion of impurities at the interface during the sintering process at such a high temperature, there is a problem that the interface is reduced to several μm and the interface becomes gentle. Particularly, in the region where the gap between the waveguides is narrow, the diffused impurities are accumulated, and the refractive index of the cladding is arbitrarily changed, so that there is a great possibility of adversely affecting the device characteristics. The deformation of the boundary due to the diffusion of impurities is closely related to the composition and thermal properties of the thin film.

In order to solve the above problems, a method of increasing the softening temperature of the undercladding layer and the core layer deposited on the substrate or lowering the sintering temperature of the upper cladding layer Can be considered. However, in order to achieve this, the impurity content in the lower cladding layer must be reduced. In this case, the difference in thermal expansion coefficient between the substrate and the silicon substrate increases, so that birefringence may increase and sintering is difficult. Further, in order to lower the sintering temperature of the upper cladding layer, the impurity content must be increased, but when it is too much, reliability of the thin film is poor.

In addition, a method of etching a silica substrate containing little impurities by etching, filling the core with a core having a large refractive index, and depositing an upper cladding layer thereon is used. However, after the core layer is deposited, And there is a difficulty in realizing a complete waveguide boundary upon deposition of the upper cladding layer.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the problems of the prior art described above, and it is an object of the present invention to provide a method of manufacturing a semiconductor device, in which a silica thin film is deposited on a surface of a lower cladding layer and an etched core surface to minimize diffusion of impurities, And a method of manufacturing the optical waveguide device, which minimizes waveguide deformation occurring at an interface for depositing a layer or depositing an upper cladding layer on an etched structure.

Another object of the present invention is to provide an optical waveguide device having at least one silica thin film and a manufacturing method thereof.

It is still another object of the present invention to provide an optical waveguide device having at least one passivation layer using a CVD method and a manufacturing method thereof.

According to an aspect of the present invention,

A lower clad layer deposited on the planar substrate;

A passivation layer deposited on the lower clad layer to minimize deformation occurring at the interface;

An optical waveguide formed on the passivation layer by patterning with a material having a refractive index higher than that of the lower cladding layer; And

And an upper cladding layer deposited on the optical waveguide and the passivation layer.

FIGS. 1A to 1F are views illustrating steps of fabricating a planar optical waveguide having a passivation layer according to a preferred embodiment of the present invention.

2 is a view showing a planar optical waveguide having a passivation layer according to another preferred embodiment of the present invention.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted so as to avoid obscuring the subject matter of the present invention.

FIGS. 1A to 1F are views sequentially illustrating steps of fabricating an optical waveguide having a passivation layer according to an embodiment of the present invention. Referring to the drawings, an optical waveguide device according to the present invention deposits a lower cladding layer 12 having a predetermined refractive index on a planar substrate 10 having a predetermined thickness. A state in which the lower clad layer 12 is deposited on the substrate 10 is shown in FIG. The planar substrate 10 is a silica substrate. Next, a first passivation layer 14 having a constant refractive index is formed on the lower clad layer 12 to be thin. A state in which the first passivation layer 14 is deposited on the lower cladding layer 12 is shown in FIG. The first passivation layer 14 refers to a thin film containing silicon dioxide (SiO ₂ ) having a high softening point and little impurities, that is, a pure silica film. The first passivation layer 14 is similar to the refractive index of the lower cladding layer 12 and has a high softening point. Since the first passivation layer 14 has a smaller amount of impurities than the lower cladding layer 12, the first passivation layer 14 minimizes the deformation due to diffusion occurring at the interface. Also, the first passivation layer 14 is formed using a chemical vapor deposition (CVD) method. The principle that the deformation due to diffusion is minimized by the first passivation layer 14 will be described below.

Next, a core layer 16 having a higher refractive index than the lower cladding layer 12 is formed on the first passivation layer 14. A state in which the core layer 16 is deposited on the first passivation layer 14 is shown in Fig. 1C. The deposited core layer 16 is etched to form a light waveguide, that is, a patterned core layer 16a. The patterned core layer 16a is shown in Figure 1d. The second passivation layer 18 is formed on the surface of the patterned core layer 16a and the first passivation layer 14 using a chemical vapor deposition (CVD) method having excellent step coverage. . The second passivation layer 18 includes a substantially pure silica thin film having a high softening point, that is, pure silicon dioxide, and is similar to the refractive index of the lower cladding layer 12. The second passivation layer 18 is deposited to surround the patterned core layer 16a. That is, the second passivation layer 18 is deposited on the top end and the side end of the patterned core layer 16a and is deposited on the first passivation layer 14. An upper cladding layer 20 having the same refractive index as that of the lower cladding layer 12 is formed on the second passivation layer 18. At this time, since the impurity content of the second passivation layer 18 is less than that of the upper cladding layer 20, the deformation due to diffusion occurring at the interface is minimized.

As described above, in the optical waveguide device according to the present invention, the patterned core layer 16a is isolated from the lower cladding layer 12 by the first passivation layer 14, and the patterned core layer 16a is formed on the second passivation layer 18 Is isolated from the upper cladding layer 20, so that deformation at the interface is minimized.

According to an embodiment of the present invention, the first passivation layer 14 is deposited to a thickness of 0.1 to 1 m, and the second passivation layer 18 is deposited to a thickness of 0.1 to 1 m.

As described above, in the optical waveguide device having the passivation layer according to the present invention, at least one passivation layer is provided to minimize the deformation occurring at the interface, as follows.

When two layers with different concentrations are heated to a high temperature, mass transfer occurs in a direction in which the concentration difference becomes smaller around the interface. When the high-temperature treatment time becomes long enough, the concentration becomes the same, and the net movement of the substance no longer occurs. The mass transfer (diffusion) rate is proportional to the concentration difference at the interface. Equation 1 of Fick's first law on diffusion is as follows.

J = -D? C

In Equation 1, J denotes a flux of a component, D denotes a diffusion coefficient, and C denotes a concentration gradient.

In Equation (1), the diffusion velocity is proportional to the diffusion coefficient. The diffusion coefficient is affected by the kind of the substance to be diffused and the density, state, and temperature of the diffusion medium. The diffusion coefficient is represented by the following equation (2).

In Equation 2,

In the case of having the same temperature and density, the diffusion rate is closely related to the state of the medium, that is, the case of silica, and the softening point which varies depending on the composition. The case of not being easily softened even at high temperature is slower than the case where softening is good. In the case of silica, the softening point is closely related. Generally, the higher the content of impurities, the lower the softening point, so it is best to reduce the impurity content in order to reduce diffusion.

In the present invention, in order to minimize the deformation of the boundary due to diffusion in the process of depositing the upper layer film when the softening point is low due to the high impurity content of the lower cladding layer 12 or the optical waveguide 16a, Layer was deposited on the lower layer film.

7, the planar optical waveguide according to another embodiment of the present invention includes a single passivation layer 14 on the lower cladding layer 12 to minimize deformation due to diffusion at the interface A planar optical waveguide is disclosed. 6 illustrates deposition of the two passivation layers 14 and 18 on the lower cladding layer 12 and the patterned core layer 16a. However, the planar optical waveguide shown in FIG. 7 includes one passivation layer 14, Is deposited on the lower cladding layer (12). Since the other explanations have already been described in detail, the detailed description will be omitted.

While the invention has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.

As described above, the present invention is advantageous in that a desired waveguide structure can be fabricated by depositing a passivation layer that minimizes the waveguide deformation due to diffusion regardless of the composition of the lower layer. Since the silica thin film deposition technique by CVD is widely used, this technique can be easily used when it is necessary to precisely control the characteristics of the designed device, precisely control the device characteristics, or reproduce it.

Claims (19)

A flat substrate; A lower clad layer deposited on the planar substrate; A passivation layer deposited on the lower clad layer to minimize deformation occurring at the interface; An optical waveguide formed by depositing and patterning a material having a refractive index higher than that of the lower cladding layer on the passivation layer; And And an upper cladding layer deposited on the optical waveguide and the passivation layer. The method according to claim 1, Wherein the passivation layer has a smaller impurity content than the lower cladding layer and the upper cladding layer, thereby minimizing waveguide deformation due to diffusion caused at the interface. The method according to claim 1, Wherein the flat substrate is a silicon substrate. The method according to claim 1, Wherein the upper cladding layer and the lower cladding layer have the same refractive index. The method according to claim 1, Wherein the passivation layer comprises silicon dioxide free of impurities. The method according to claim 1, And the thickness of the passivation layer is 0.1 to 1 占 퐉. The method according to claim 1, Wherein the passivation layer is formed using chemical vapor deposition. A flat substrate; A lower clad layer deposited on the planar substrate; A first passivation layer deposited on the lower clad layer to minimize deformation occurring at the interface; An optical waveguide formed by depositing and patterning on the first passivation layer with a material having a refractive index higher than that of the lower cladding layer; A second passivation layer deposited on the optical waveguide and the first passivation layer; And And an upper cladding layer deposited on the second passivation layer. 9. The method of claim 8, Wherein the first and second passivation layers have fewer impurities than the lower cladding layer and the upper cladding layer, thereby minimizing waveguide deformation caused by diffusion at the interface. 9. The method of claim 8, Wherein the flat substrate is a silicon substrate. 9. The method of claim 8, And the upper cladding layer and the lower cladding layer have the same refractive index. 9. The method of claim 8, Wherein the first and second passivation layers include pure silicon dioxide free from impurities. 9. The method of claim 8, And the second passivation layer surrounds the optical waveguide layer to deposit the second optical waveguide layer. 9. The method of claim 8, And the thickness of the first and second passivation layers is 0.1 to 1 占 퐉. 9. The method of claim 8, Wherein the first and second passivation layers are formed using chemical vapor deposition. (a) depositing a lower cladding layer having a constant refractive index on a planar substrate; (b) depositing a passivation layer on the lower cladding layer to a predetermined thickness; (c) depositing a core layer having a refractive index higher than that of the lower cladding layer on the passivation layer; (d) patterning the core layer and etching the core layer to form an optical waveguide; And (e) depositing an upper cladding layer having a constant refractive index on the optical waveguide and the passivation layer. 17. The method of claim 16, Further comprising the step of depositing another passivation layer between the step (d) and the step (e). The method according to claim 16 or 17, Wherein the passivation layer has a thickness of 0.1 to 1 占 퐉. 18. The method according to claim 16 or 17, Wherein the passivation layer is deposited using a chemical vapor deposition method.